1. Field of the Invention
This invention relates to certain novel asymmetric triorganotin compounds containing two substituted phenyl groups bonded to the tin atom and to the use of these compounds as fungicides.
2. Description of the Prior Art
Asymmetric triorganotin halides of the general formula R.sup.1 R.sup.2 R.sup.3 SnX wherein each R is a hydrocarbyl group are disclosed in the prior art. German Offenlegungschrift No. 2,608,698 discloses a method for preparing this class of compounds by reacting a tetraorganotin compound of the general formula R.sup.1 R.sup.2 SnR.sub.2.sup.3 with a diorganotin dihalide of the formula R.sup.1 R.sup.2 SnX.sub.2. The reaction is conducted at temperatures from 50.degree. to 250.degree. C. in the presence of a Lewis acid catalyst such as boron trifluoride or aluminum trichloride. In accordance with this teaching triorganotin compounds containing two phenyl and one alkyl group, such as diphenylmethyltin chloride, can be prepared by reacting diphenyltin dichloride with triphenylmethyltin, yielding equimolar amounts of triphenyltin chloride and the desired product, diphenylmethyltin chloride. Example 12 of the aforementioned publication discloses that the two products can be separated by recrystallization from hexane. The desired product is soluble and the by-product precipitates and can be removed by filtration. Depending upon the solubility product of the by-product, triphenyltin chloride, the desired compounds may still contain significant amounts of by-product. More importantly, the yield of desired compound cannot exceed 50 mole %, based on the total moles of tine present in the original reaction mixture. If substituents are present on the phenyl ring, it may not be possible to separate the two organotin halides by selective precipitation. It is well known that the presence of substituents on a phenyl ring of a triorganotin compound can alter the solubility and other physical properties of the compound. It may therefore be impossible to prepare triorganotin compounds containing two substituted phenyl groups bonded to the tin atom in the absence of the corresponding tri(substituted phenyl)tin compound using the method disclosed in German Offenlegungschrift No. 2,608,698.
Japanese Patent Publication 13261/65 discloses a number of asymmetric triorganotin compounds containing one or two substituted phenyl groups that are allegedly effective stabilizers for polypropylene. Two general preparative method are: (1) the reaction of a diorganotin dihalide with an organomagnesium halide and (2) cleavage of the corresponding tetraorganotin compounds with a halogen. The two methods are disclosed as being equivalent and there are no examples showing preparation of specific compounds. The first general method is not suitable for compounds containing two phenyl groups bonded to tin, since it will yield mixtures containing the desired product with the corresponding di- and tetraorganotin compounds. These mixtures may not be separable to obtain the desired product. The second method may yield one or more undesirable by-products, depending upon the tetraorganotin compound and the reaction conditions. Compounds of the formula ##STR3## wherein (1) R.sup.1 is ethyl and x is halogen and (2) R.sup.1 is cyclohexyl and x is halogen or ##STR4## as disclosed in this publication.
It has now been discovered that bis(substituted phenyl)alkyltin compounds can be prepared in the absence of significant amounts of di- and tetraorganotin compounds and the corresponding tri(substituted phenyl)tin compounds. Some of these bis(substituted phenyl alkyltin compounds are novel, and constitute part of this invention.